Explosionproof candy thermometer

ABSTRACT

A candy thermometer is made explosionproof by forming the outer protective tube with an open upper end which is closed by means of a plastic cap which normally is frictionally but removably held in sealing relation and which softens and distorts before the temperature and hence the pressure of the air in the tube exceed safe limits, thereby relieving the internal air pressure.

United States Patent [151 3,636,769

Chaney 1 Jan. 25, 1972 [54] EXPLOSIONPROOF CANDY 3,527,102 9/1970Harland ..73/416 X 2,389,485 11/1945 Bruns.....

THERMOMETER 2,672,053 3/1954 Geyer.... [72] Inventor: John L. Chaney,Lake Geneva, Wis. 3,484,016 12/1969 Turner ..215/41 53147 PrimaryExaminer-Louis R. Prince [22] Flled 1970 Assistant ExaminerDaniel M.Yasich [21] Appl. No.: 23,815 Att0rney--Marechal, Biebel, French & Eng

[57] ABSTRACT [52] US. CL... ..73/371, 73/374 [5 1] Int. Cl. ..G0lk1/12A candy thermometer i a e xplosionproof by forming the [58] Field ofSearch ..73/371, 374, 378, 416; outer protective tube wi an p n pp r endwhich is clo ed 206/165; 215/41; 220/44 by means of a plastic cap whichnormally is frictionally but removably held in sealing relation andwhich softens and [56] References Cit d distorts before the temperatureand hence the pressure of the air in the tube exceed safe limits,thereby relieving the internal UNITED STATES PATENTS air pressure.

1,995,470 3/1935 Chaney ..73/378 3 Claims, 3 Drawing Figures 3,273,3949/1966 Chaney ..73/374 PATENTED JANZS m2 FIG-3 FIG-l //V VEN TOR JOHN L.CHANEY ATTORNEYS EXPLOSIONPROOF CANDY THERMOMETER BACKGROUND OF THEINVENTION A conventional candy thermometer includes a graduated scalecard to which the thermometer tube is fastened and an outer protectivetube so that when dipped in the candy the scale card and thermometertube do not come in contact with the candy. The tube is usually sealedat the top and bottom to make certain that the interior of the tube iskept completely clean.

In its normal use the thermometer is clipped to the side of the cookingpan and the majority of its length is in the room atmosphere so that noundue heating occurs. However at times the thermometer is put into theoven and the oven temperature raised as a means of checking thethermostat. Thus the entire body of the thermometer under theseconditions can be subjected to temperature of the order of 400 to 550 F.When this occurs there is an increase of internal pressure of the orderof 1 atmosphere, i.e., from about 12 to 14 pounds per square inch.Ordinarily the tube can withstand this pressure but it it is struck oris dropped, it may shatter with explosive force.

In my prior U.S. Pat. No. 1,995 ,470, I disclose a candy thermometer inwhich the upper end of the outer tube is open, and is closed by a rubbercap. This construction does not assure an explosionproof product howeverbecause the rubber has different characteristics from the plastic capused in the present invention. It may over a period of time undergovulcanization such as to be firmly fastened in place, and in additionrubber has different characteristics under increase in temperature anddoes not function to relieve internal pressure as does the plasticmaterial used in the present invention.

SUMMARY OF THE INVENTION In accordance with the present invention theopen upper end of the protective tube of a candy thermometer is closedby a plastic cap which fits sufficiently securely during the normal useof the thermometer to fully protect the interior against entranceof anyforeign matter but which is of such character that it will soften as thetemperature approaches the boiling point and thus will relieve theinternal pressure before it exceeds safe limits, thus rendering thethermometer explosionproof.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 shows a front view of thethermometer in accordance with the present invention;

FIG. 2 is a side view with the upper portion of the protective tube andthe cap being shown in section on the line 22 of FIG. 1; and

FIG. 3 is a view in perspective on a larger scale of the upper end ofthe thermometer showing the cap removed.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 of the drawing shows thegraduated scale card on which the thermometer tube 11 is mounted bymeans of fasteners 12. The card and thermometer are enclosed in an outerprotective tube 15 with the bulb of the thermometer extending down tothe lower end of the tube in good heat conducting relationship with ametal cap 16 at the lower end. A disk I7 is mounted on the upper end ofthe scale card to maintain the scale card and thermometer tube in acentral position within the outer tube.

A spring clip 20 is slidably received on the outer surface of the tube15 and includes a spring arm 2I to fasten the thermometer in uprightposition over the edge of a cooking pan.

The upper end of tube 15 is open as shown at 25 in FIG. 3 and a cap 26is adapted to be frictionally received over the open end. Cap 26 is madeof plastic material of the thermoplastic type such as polyethylene andis selected so that while it fully protects and seals the end of thetube under normal atmospheric temperature conditions, it will, whenheated to a temperature approaching the boiling point of water, softenand distort enough to allow escape of air pressure developed within thetube. Polyethylene for example can be used advantageously which softensat F. and which will actually melt at a temperature approaching 250Thermosetting materials or elastomers of the rubber-type either do notdistort or seal more tightly to the tube; other thermoplastic materialswhich may be used are polyolefines such as polypropylene and copolymersthereof or mixtures thereof. Also, while the device has been referred toas a candy thermometer its use is not limited to candy, as it mayequally well be used for deep fat and other types of cooking carried outin a pan.

In normal operations such temperatures are never encountered but in somecases the user may want to check the calibration of the oven thermostatand when this occurs the entire thermometer is placed in the oven. Ifthe temperature of the oven is raised toward 400'-550 F., a substantialpressure of the order of 12 to 14 pounds per square inch would developin the tube if the tube remained sealed. However with the thermometer ofthe present invention, before such temperature is reached, the plasticcap will have softened enough to relieve the internal air pressure andthus no matter how high it is heated, it is rendered explosionproof.

While the form of device herein described constitutes a preferredembodiment of the invention it is to be understood that the invention isnot limited to this precise form and that changes may be made thereinwithout departing from the scope of the invention which is defined inthe appended claims.

What is claimed is:

1. An explosionproof candy thermometer capable of being heated in anoven up to of the order of 400-550 F. without danger of exploding evenif struck or dropped, comprising a graduated scale card, a thermometertube fastened in place on said scale card and having a heat-sensitivebulb at its lower end, a protective glass tube enclosing said card andsaid thermometer tube, said protective tube having a closed bottom endin close heat transmitting relation with said thermometer bulb andhaving an open top end, and a cup-shaped plastic cap of thermoplasticmaterial closing said open top end and being frictionally received onthe outer surface of the upper end of said tube in normally sealingrelation, said cap having the capacity of softening and distorting underheating of the tube thereby relieving internal air pressure in the tubebefore such pressure exceeds safe limits.

2. A thermometer as defined in claim 1 in which the plastic ispolyethylene.

3. A thermometer as defined in claim 2 in which the plastic material isone which will soften at an elevated temperature approaching the boilingpoint of water.

1. An explosionproof candy thermometer capable of being heated in anoven up to of the order of 400*-550* F. without danger of exploding evenif struck or dropped, comprising a graduated scale card, a thermometertube fastened in place on said scale card and having a heat-sensitivebulb at its lower end, a protective glass tube enclosing said card andsaid thermometer tube, said protective tube having a closed bottom endin close heat transmitting relation with said thermometer bulb andhaving an open top end, and a cup-shaped plastic cap of thermoplasticmaterial closing said open top end and being frictionally received onthe outer surface of the upper end of said tube in normally sealingrelation, said cap having the capacity of softening and distorting underheating of the tube thereby relieving internal air pressure in the tubebefore such pressure exceeds safe limits.
 2. A thermometer as defined inclaim 1 in which the plastic is polyethylene.
 3. A thermometer asdefined in claim 2 in which the plastic material is one which willsoften at an elevated temperature approaching the boiling point ofwater.